The optically active octanoic acid derivatives prepared by the present invention are intermediates useful for the preparation of medicaments or are compounds useful as medicaments. For example, a racemate of 2R-propyloctanoic acid is described in Example 7(33) of JP-A-7-316092 as an agent for treating or preventing neurodegenerative diseases derived from functional abnormality of astrocytes.
As a result of the study after that, it was found that optically active 2R-propyloctanoic acid has strong activities in particular. Accordingly, methods for obtaining this compound efficiently have been studied variously, and the following processes are known until now.
For example, JP-A-8-291106 discloses a method by optical resolution using optically active amine. However, in the process of optically separating 2R-propyloctanoic acid from its racemate, both the chemical yield (total synthetic yield of 5.9% at 6 stages from dimethyl hexylmalonate) and the optically purity (90.0% e.e.) were so insufficient that the process had no practical use.
A process using an optically active starting material is known as other process for obtaining optically active 2R-propyloctanoic acid. For example, JP-A-8-295648 discloses a process using optically active prolinol. An optically active branched alkanoic acid having a high optical purity (96.0% e.e.) can be prepared using this process. However, the chemical yield (total synthetic yield of 20.1% at 5 stages from pentanoyl chloride) was so insufficient that the process did not necessarily have a practical use.